Upon receipt of a query message including an unrecognized mandatory
TLV object, the recipient MUST respond with an Unsupported Mandatory
TLV Object error code.

It should say:

In this specification an object that is classed as mandatory is
one that the responder MUST either support or respond to indicating
that it does not support. Thus upon receipt of a query message
including an unrecognized mandatory TLV object, the recipient
MUST respond with an Unsupported Mandatory TLV Object error
code. Note that the term mandatory does not indicate mandatory
to implement or mandatory to send.

Notes:

In discussion on the MPLS list there was concern about the meaning
of the term "mandatory" in this RFC. The use of the term is
somewhat unusual in an IETF context, but the quoted original
text makes it clear that there is no requirement to implement
mandatory objects, only to respond to the reception of one if
it is not supported.